The subject matter described herein relates to optic assemblies and, more particularly, to optic assemblies utilizing quantum dots.
White LEDs may be produced as cool white LEDs or warm white LEDs. The warmth or coolness of an LED is expressed as a color temperature in degrees Kelvin. These white LEDs typically create the white color by using a blue LED (hereafter referred to as a cool LED) with specific combination of yellow & red phosphors in close proximity to the LED. Counterintuitively, cool white LEDs produce light at the blue end of the visible spectrum and are specified in higher color temperatures, typically in excess of 5000° K whereas, warm light LEDs produce light having a higher wavelength at the red end of the visible spectrum with corresponding lower color temperatures on the order of 2700° K. The choice to use cool white LEDs or warm white LEDs may depend on the function of the light, the environment in which the light is being installed, and/or cultural differences. For example, some cultures prefer cool light sources, whereas, in other cultures, for example, North America, warm light is more preferred. However, cool white LEDs generally have a greater efficiency than warm white LEDs. For example, cool white LEDs may be as much as 35% more efficient than warm white LEDs. Accordingly, it is desirable to have cool white LEDs that can be altered to produce warm light while maintaining the efficiency of the cool white LED.
Quantum dots are semiconductor nanocrystals on the order of 2-10 nanometers in size that alter the wavelength of light as it passes through the quantum dot. When incoming light with sufficient energy strikes a quantum dot, it temporarily displaces an electron from the valence band across a band gap into the higher adjacent conducive band creating a corresponding positively charged hole in the valence band. In this unstable state, the electron drops back to the valence band and in the process emits energy in the form of light. The specific wavelength of the reemitted light is determined from bandgap and size of the quantum dot. For example, larger quantum dots shift incoming wavelengths to lower energy light at a higher wavelength. Accordingly, a larger quantum dot shifts incoming wavelengths towards the red end of the visible spectrum. Conversely, smaller quantum dots emit higher energy light at a smaller wavelength. Smaller quantum dots shift incoming wavelengths at the blue end of the visible spectrum. As such, quantum dots may be used with lighting to adjust a color of the light emitted. In a typical example, a monochromatic blue light source such as an LED may be coated with quantum dots to adjust the energy or the wavelength of the light emitted therefrom, thereby warming the cool light.
However, quantum dots are not without their disadvantages. Particularly, quantum dots may break down and degrade when exposed to high temperatures. As such the use of quantum dots with lighting is limited to low power lights which emit a minimal amount of conducted and radiated heat. High power lights and in particular LEDs, on the other hand, are not capable of being used with quantum dots because the heat from the high power LED will quickly degrade the quantum dots.
Moreover, high power LEDs are generally cheaper and easier to manufacture as cool white LEDs. However, at the time of installation, a warm light may be desired. Because high power LEDs in close proximity to the quantum dots degrade the quantum dots, the use of quantum dots to warm the light from a high power, cool LED is not an option.
A need remains for a high power cool LED that can be warmed by quantum dots, while maintaining the efficiency of the cool LED.